diff --git a/Sources/BeaconChain/BeaconChain.swift b/Sources/BeaconChain/BeaconChain.swift
index e825da1..a847d67 100644
--- a/Sources/BeaconChain/BeaconChain.swift
+++ b/Sources/BeaconChain/BeaconChain.swift
@@ -273,62 +273,6 @@ extension BeaconChain {
 
 extension BeaconChain {
 
-    static func verifySlashableAttestation(state: BeaconState, slashableAttestation: SlashableAttestation) -> Bool {
-        if slashableAttestation.custodyBitfield != Data(repeating: 0, count: slashableAttestation.custodyBitfield.count) {
-            return false
-        }
-
-        if slashableAttestation.validatorIndices.count == 0 {
-            return false
-        }
-
-        for i in 0..<(slashableAttestation.validatorIndices.count - 1) {
-            if slashableAttestation.validatorIndices[i] >= slashableAttestation.validatorIndices[i + 1] {
-                return false
-            }
-        }
-
-        if !verifyBitfield(bitfield: slashableAttestation.custodyBitfield, committeeSize: slashableAttestation.validatorIndices.count) {
-            return false
-        }
-
-        if slashableAttestation.validatorIndices.count > MAX_INDICES_PER_SLASHABLE_VOTE {
-            return false
-        }
-
-        var custodyBit0Indices = [UInt64]()
-        var custodyBit1Indices = [UInt64]()
-
-        for (i, validatorIndex) in slashableAttestation.validatorIndices.enumerated() {
-            if getBitfieldBit(bitfield: slashableAttestation.custodyBitfield, i: i) == 0b0 {
-                custodyBit0Indices.append(validatorIndex)
-            } else {
-                custodyBit1Indices.append(validatorIndex)
-            }
-        }
-
-        return BLS.verify(
-            pubkeys: [
-                BLS.aggregate(
-                    pubkeys: custodyBit0Indices.map { (i) in
-                        return state.validatorRegistry[Int(i)].pubkey
-                    }
-                ),
-                BLS.aggregate(
-                    pubkeys: custodyBit1Indices.map { (i) in
-                        return state.validatorRegistry[Int(i)].pubkey
-                    }
-                )
-            ],
-            messages: [
-                hashTreeRoot(AttestationDataAndCustodyBit(data: slashableAttestation.data, custodyBit: false)),
-                hashTreeRoot(AttestationDataAndCustodyBit(data: slashableAttestation.data, custodyBit: true)),
-            ],
-            signature: slashableAttestation.aggregateSignature,
-            domain: getDomain(fork: state.fork, epoch: slashableAttestation.data.slot.toEpoch(), domainType: Domain.ATTESTATION)
-        )
-    }
-
     static func isDoubleVote(_ left: AttestationData, _ right: AttestationData) -> Bool {
         return left.slot.toEpoch() == right.slot.toEpoch()
     }
diff --git a/Sources/BeaconChain/DataStructures/Transactions/AttesterSlashings/SlashableAttestation.swift b/Sources/BeaconChain/DataStructures/Transactions/AttesterSlashings/SlashableAttestation.swift
index 47efd6d..722d846 100644
--- a/Sources/BeaconChain/DataStructures/Transactions/AttesterSlashings/SlashableAttestation.swift
+++ b/Sources/BeaconChain/DataStructures/Transactions/AttesterSlashings/SlashableAttestation.swift
@@ -5,4 +5,60 @@ struct SlashableAttestation {
     let data: AttestationData
     let custodyBitfield: Data
     let aggregateSignature: Data
+
+    func verify(state: BeaconState) -> Bool {
+        if custodyBitfield != Data(repeating: 0, count: custodyBitfield.count) {
+            return false
+        }
+
+        if validatorIndices.count == 0 {
+            return false
+        }
+
+        for i in 0..<(validatorIndices.count - 1) {
+            if validatorIndices[i] >= validatorIndices[i + 1] {
+                return false
+            }
+        }
+
+        if !BeaconChain.verifyBitfield(bitfield: custodyBitfield, committeeSize: validatorIndices.count) {
+            return false
+        }
+
+        if validatorIndices.count > MAX_INDICES_PER_SLASHABLE_VOTE {
+            return false
+        }
+
+        var custodyBit0Indices = [UInt64]()
+        var custodyBit1Indices = [UInt64]()
+
+        for (i, validatorIndex) in validatorIndices.enumerated() {
+            if BeaconChain.getBitfieldBit(bitfield: custodyBitfield, i: i) == 0b0 {
+                custodyBit0Indices.append(validatorIndex)
+            } else {
+                custodyBit1Indices.append(validatorIndex)
+            }
+        }
+
+        return BLS.verify(
+            pubkeys: [
+                BLS.aggregate(
+                    pubkeys: custodyBit0Indices.map { (i) in
+                        return state.validatorRegistry[Int(i)].pubkey
+                    }
+                ),
+                BLS.aggregate(
+                    pubkeys: custodyBit1Indices.map { (i) in
+                        return state.validatorRegistry[Int(i)].pubkey
+                    }
+                )
+            ],
+            messages: [
+                BeaconChain.hashTreeRoot(AttestationDataAndCustodyBit(data: data, custodyBit: false)),
+                BeaconChain.hashTreeRoot(AttestationDataAndCustodyBit(data: data, custodyBit: true)),
+            ],
+            signature: aggregateSignature,
+            domain: BeaconChain.getDomain(fork: state.fork, epoch: data.slot.toEpoch(), domainType: Domain.ATTESTATION)
+        )
+    }
 }
diff --git a/Sources/BeaconChain/StateTransition.swift b/Sources/BeaconChain/StateTransition.swift
index aac73d6..c059139 100644
--- a/Sources/BeaconChain/StateTransition.swift
+++ b/Sources/BeaconChain/StateTransition.swift
@@ -133,8 +133,8 @@ extension StateTransition {
                     || BeaconChain.isSurroundVote(slashableAttestation1.data, slashableAttestation2.data)
             )
 
-            assert(BeaconChain.verifySlashableAttestation(state: state, slashableAttestation: slashableAttestation1))
-            assert(BeaconChain.verifySlashableAttestation(state: state, slashableAttestation: slashableAttestation2))
+            assert(slashableAttestation1.verify(state: state))
+            assert(slashableAttestation2.verify(state: state))
 
             let slashableIndices = slashableAttestation1.validatorIndices.filter {
                 slashableAttestation2.validatorIndices.contains($0)