diff --git a/codex/blockexchange/swarm.nim b/codex/blockexchange/swarm.nim
index 0cf638b7..0a838504 100644
--- a/codex/blockexchange/swarm.nim
+++ b/codex/blockexchange/swarm.nim
@@ -63,6 +63,7 @@ type
     # Network interface
     network*: BlockExcNetwork
     discovery*: Discovery
+    peerEventHandler: PeerEventHandler
 
     completionHandle: Future[?!void]
 
@@ -217,15 +218,6 @@ proc loadBlockKnowledge*(self: Swarm): Future[void] {.async: (raises: []).} =
 
   self.updateDownloadedBlocks(totalBlocks)
 
-proc start*(self: Swarm): Future[void] {.async: (raises: []).} =
-  trace "Initialize swarm. Load block knowledge.", cid = self.cid
-  await self.loadBlockKnowledge()
-
-  trace "Joining swarm."
-  # Bootstraps
-  self.trackedFutures.track(self.neighborMaintenanceLoop())
-  self.trackedFutures.track(self.advertiseLoop())
-
 proc sendBlockRequests(
     self: Swarm, peer: PeerId, requests: seq[int]
 ) {.async: (raw: true).} =
@@ -464,6 +456,102 @@ proc dropPeer*(self: Swarm, peer: PeerId) {.raises: [].} =
   # drop the peer from the peers table
   self.peers.del(peer)
 
+# Since this is all very fragile, we add checks to make sure the messages we're
+# getting are for the right swarm. This is especially important as we run iterated
+# experiments and replace the handlers for each new download.
+proc checkBlockAddress(self: Swarm, address: BlockAddress): bool =
+  if address.leaf:
+    return address.treeCid == self.manifest.treeCid
+  else:
+    return address.cid == self.manifest.treeCid
+
+proc checkAddresses[T](self: Swarm, messages: seq[T]): bool =
+  return messages.allIt(checkBlockAddress(self, it.address))
+
+proc installEventHandlers(self: Swarm) =
+  proc peerEventHandler(
+      peerId: PeerId, event: PeerEvent
+  ): Future[void] {.gcsafe, async: (raises: [CancelledError]).} =
+    if event.kind == PeerEventKind.Joined:
+      await self.setupPeer(peerId)
+    else:
+      self.dropPeer(peerId)
+
+  self.peerEventHandler = peerEventHandler
+
+  proc wantListHandler(peer: PeerId, wantList: WantList) {.async: (raises: []).} =
+    if not self.checkAddresses(wantList.entries):
+      return
+
+    if wantList.full:
+      await self.handleBlockKnowledgeRequest(peer)
+    else:
+      await self.handleBlockRequest(peer, wantList.entries.mapIt(it.address).toSeq)
+
+  proc blocksPresenceHandler(
+      peer: PeerId, presence: seq[BlockPresence]
+  ) {.async: (raises: []).} =
+    if not self.checkAddresses(presence):
+      return
+
+    self.handleBlockKnowledgeResponse(peer, presence)
+
+  proc blocksDeliveryHandler(
+      peer: PeerId, blocksDelivery: seq[BlockDelivery]
+  ): Future[void] {.async: (raises: []).} =
+    if not self.checkAddresses(blocksDelivery):
+      return
+    self.handleBlockDelivery(peer, blocksDelivery)
+
+  if not isNil(self.network.switch):
+    self.network.switch.addPeerEventHandler(self.peerEventHandler, PeerEventKind.Joined)
+    self.network.switch.addPeerEventHandler(self.peerEventHandler, PeerEventKind.Left)
+
+  self.network.handlers = BlockExcHandlers(
+    onWantList: wantListHandler,
+    onBlocksDelivery: blocksDeliveryHandler,
+    onPresence: blocksPresenceHandler,
+    onAccount: nil,
+    onPayment: nil,
+  )
+
+proc uninstallEventHandlers(self: Swarm) =
+  if not isNil(self.network.switch):
+    self.network.switch.removePeerEventHandler(
+      self.peerEventHandler, PeerEventKind.Joined
+    )
+    self.network.switch.removePeerEventHandler(
+      self.peerEventHandler, PeerEventKind.Left
+    )
+
+  self.network.handlers = BlockExcHandlers(
+    onWantList: nil,
+    onBlocksDelivery: nil,
+    onPresence: nil,
+    onAccount: nil,
+    onPayment: nil,
+  )
+
+proc start*(self: Swarm): Future[void] {.async: (raises: []).} =
+  trace "Initialize swarm. Load block knowledge.", cid = self.cid
+  await self.loadBlockKnowledge()
+
+  trace "Joining swarm."
+  self.installEventHandlers()
+  # Bootstraps
+  self.trackedFutures.track(self.neighborMaintenanceLoop())
+  self.trackedFutures.track(self.advertiseLoop())
+
+proc stop*(self: Swarm): Future[void] {.async: (raises: []).} =
+  trace "Stopping event loops and uninstalling handlers"
+  # We should probably have a way to actively inform the DHT tracker
+  # that we're leaving.
+  await self.trackedFutures.cancelTracked()
+  # Messages that arrive after this will be ignored (or
+  # might be delivered to another swarm if we restart a download).
+  self.uninstallEventHandlers()
+  trace "Left swarm"
+
 proc new*(
     T: type Swarm,
     dataset: Manifest,
@@ -471,7 +559,7 @@ proc new*(
     network: BlockExcNetwork,
     discovery: Discovery,
 ): Swarm =
-  let self = Swarm(
+  return Swarm(
     manifest: dataset,
     localStore: localStore,
     network: network,
@@ -484,41 +572,3 @@ proc new*(
     trackedFutures: TrackedFutures.new(),
     completionHandle: newFuture[?!void]("codex.blockexchange.swarm.start"),
   )
-
-  proc peerEventHandler(
-      peerId: PeerId, event: PeerEvent
-  ): Future[void] {.gcsafe, async: (raises: [CancelledError]).} =
-    if event.kind == PeerEventKind.Joined:
-      await self.setupPeer(peerId)
-    else:
-      self.dropPeer(peerId)
-
-  proc wantListHandler(peer: PeerId, wantList: WantList) {.async: (raises: []).} =
-    if wantList.full:
-      await self.handleBlockKnowledgeRequest(peer)
-    else:
-      await self.handleBlockRequest(peer, wantList.entries.mapIt(it.address).toSeq)
-
-  proc blocksPresenceHandler(
-      peer: PeerId, presence: seq[BlockPresence]
-  ) {.async: (raises: []).} =
-    self.handleBlockKnowledgeResponse(peer, presence)
-
-  proc blocksDeliveryHandler(
-      peer: PeerId, blocksDelivery: seq[BlockDelivery]
-  ): Future[void] {.async: (raises: []).} =
-    self.handleBlockDelivery(peer, blocksDelivery)
-
-  if not isNil(network.switch):
-    network.switch.addPeerEventHandler(peerEventHandler, PeerEventKind.Joined)
-    network.switch.addPeerEventHandler(peerEventHandler, PeerEventKind.Left)
-
-  network.handlers = BlockExcHandlers(
-    onWantList: wantListHandler,
-    onBlocksDelivery: blocksDeliveryHandler,
-    onPresence: blocksPresenceHandler,
-    onAccount: nil,
-    onPayment: nil,
-  )
-
-  return self
diff --git a/codex/node.nim b/codex/node.nim
index 482ed6f9..70e624c5 100644
--- a/codex/node.nim
+++ b/codex/node.nim
@@ -120,6 +120,17 @@ proc downloadStatus*(self: CodexNodeRef, dataset: Cid): ?(int, int) =
   except KeyError:
     return none((int, int))
 
+proc stopDownload*(self: CodexNodeRef, dataset: Cid): Future[?!void] {.async.} =
+  ## Stop a download for a manifest
+  ##
+  if dataset notin self.downloads:
+    return success()
+
+  await self.downloads[dataset].stop()
+
+  self.downloads.del(dataset)
+  return success()
+
 proc storeManifest*(
     self: CodexNodeRef, manifest: Manifest
 ): Future[?!bt.Block] {.async.} =
diff --git a/codex/rest/api.nim b/codex/rest/api.nim
index 3b34aecc..8ff941a0 100644
--- a/codex/rest/api.nim
+++ b/codex/rest/api.nim
@@ -222,6 +222,19 @@ proc initDataApi(node: CodexNodeRef, repoStore: RepoStore, router: var RestRoute
     else:
       return RestApiResponse.error(Http404)
 
+  router.rawApi(MethodDelete, "/api/codex/v1/download/{cid}") do(
+    cid: Cid, resp: HttpResponseRef
+  ) -> RestApiResponse:
+    let downloadId = cid.get()
+    if downloadId notin node.downloads:
+      return RestApiResponse.error(Http404)
+
+    if err =? (await node.stopDownload(downloadId)).errorOption:
+      return RestApiResponse.error(Http500, err.msg)
+
+    resp.status = Http204
+    await resp.sendBody("")
+
   router.rawApi(MethodPost, "/api/codex/v1/data") do() -> RestApiResponse:
     ## Upload a file in a streaming manner
     ##