diff --git a/packages/beacon-node/src/chain/blocks/importBlock.ts b/packages/beacon-node/src/chain/blocks/importBlock.ts
index 6c28e020873b..6ab0b2867d96 100644
--- a/packages/beacon-node/src/chain/blocks/importBlock.ts
+++ b/packages/beacon-node/src/chain/blocks/importBlock.ts
@@ -147,6 +147,7 @@ export async function importBlock(
 
     for (const attestation of attestations) {
       try {
+        // TODO Electra: figure out how to reuse the attesting indices computed from state transition
         const indexedAttestation = postState.epochCtx.getIndexedAttestation(fork, attestation);
         const {target, beaconBlockRoot} = attestation.data;
 
diff --git a/packages/beacon-node/test/spec/presets/fork_choice.test.ts b/packages/beacon-node/test/spec/presets/fork_choice.test.ts
index 9670bf6e0d9b..5e237828ef1f 100644
--- a/packages/beacon-node/test/spec/presets/fork_choice.test.ts
+++ b/packages/beacon-node/test/spec/presets/fork_choice.test.ts
@@ -136,7 +136,7 @@ const forkChoiceTest =
               const headState = chain.getHeadState();
               const attDataRootHex = toHexString(ssz.phase0.AttestationData.hashTreeRoot(attestation.data));
               chain.forkChoice.onAttestation(
-                headState.epochCtx.getIndexedAttestation(ForkSeq.phase0, attestation),
+                headState.epochCtx.getIndexedAttestation(ForkSeq[fork], attestation),
                 attDataRootHex
               );
             }
diff --git a/packages/state-transition/src/block/processAttestationPhase0.ts b/packages/state-transition/src/block/processAttestationPhase0.ts
index e4b206c66697..9cd1823e4dd4 100644
--- a/packages/state-transition/src/block/processAttestationPhase0.ts
+++ b/packages/state-transition/src/block/processAttestationPhase0.ts
@@ -2,6 +2,7 @@ import {toHexString} from "@chainsafe/ssz";
 import {Slot, allForks, electra, phase0, ssz} from "@lodestar/types";
 
 import {MIN_ATTESTATION_INCLUSION_DELAY, SLOTS_PER_EPOCH, ForkSeq} from "@lodestar/params";
+import {assert} from "@lodestar/utils";
 import {computeEpochAtSlot} from "../util/index.js";
 import {CachedBeaconStatePhase0, CachedBeaconStateAllForks} from "../types.js";
 import {isValidIndexedAttestation} from "./index.js";
@@ -89,9 +90,7 @@ export function validateAttestation(
   }
 
   if (fork >= ForkSeq.electra) {
-    if (data.index !== 0) {
-      throw new Error(`AttestationData.index must be zero: index=${data.index}`);
-    }
+    assert.equal(data.index, 0, `AttestationData.index must be zero: index=${data.index}`);
     const attestationElectra = attestation as electra.Attestation;
     const committeeBitsLength = attestationElectra.committeeBits.bitLen;
 
@@ -101,7 +100,7 @@ export function validateAttestation(
       );
     }
 
-    // TODO Electra: this should be obsolete soon when we switch to committeeIndices
+    // TODO Electra: this should be obsolete soon when the spec switches to committeeIndices
     const committeeIndices = attestationElectra.committeeBits.getTrueBitIndexes();
 
     // Get total number of attestation participant of every committee specified
@@ -109,11 +108,11 @@ export function validateAttestation(
       .map((committeeIndex) => epochCtx.getBeaconCommittee(data.slot, committeeIndex).length)
       .reduce((acc, committeeSize) => acc + committeeSize, 0);
 
-    if (attestationElectra.aggregationBits.bitLen !== participantCount) {
-      throw new Error(
-        `Attestation aggregation bits length does not match total number of committee participant aggregationBitsLength=${attestation.aggregationBits.bitLen} participantCount=${participantCount}`
-      );
-    }
+    assert.equal(
+      attestationElectra.aggregationBits.bitLen,
+      participantCount,
+      `Attestation aggregation bits length does not match total number of committee participant aggregationBitsLength=${attestation.aggregationBits.bitLen} participantCount=${participantCount}`
+    );
   } else {
     if (!(data.index < committeeCount)) {
       throw new Error(
diff --git a/packages/state-transition/src/cache/epochCache.ts b/packages/state-transition/src/cache/epochCache.ts
index 1defb036513d..3d73a58e509b 100644
--- a/packages/state-transition/src/cache/epochCache.ts
+++ b/packages/state-transition/src/cache/epochCache.ts
@@ -653,21 +653,17 @@ export class EpochCache {
    * Return the beacon committee at slot for index.
    */
   getBeaconCommittee(slot: Slot, index: CommitteeIndex): Uint32Array {
-    const slotCommittees = this.getShufflingAtSlot(slot).committees[slot % SLOTS_PER_EPOCH];
-    if (index >= slotCommittees.length) {
-      throw new EpochCacheError({
-        code: EpochCacheErrorCode.COMMITTEE_INDEX_OUT_OF_RANGE,
-        index,
-        maxIndex: slotCommittees.length,
-      });
-    }
-    return slotCommittees[index];
+    return this.getBeaconCommittees(slot, [index]);
   }
 
   /**
    * Return a single Uint32Array representing concatted committees of indices
    */
   getBeaconCommittees(slot: Slot, indices: CommitteeIndex[]): Uint32Array {
+    if (indices.length === 0) {
+      throw new Error("Attempt to get committees without providing CommitteeIndex");
+    }
+
     const slotCommittees = this.getShufflingAtSlot(slot).committees[slot % SLOTS_PER_EPOCH];
     const committees = [];
 
@@ -682,6 +678,11 @@ export class EpochCache {
       committees.push(slotCommittees[index]);
     }
 
+    // Early return if only one index
+    if (committees.length === 1) {
+      return committees[0];
+    }
+
     // Create a new Uint32Array to flatten `committees`
     const totalLength = committees.reduce((acc, curr) => acc + curr.length, 0);
     const result = new Uint32Array(totalLength);
@@ -807,13 +808,12 @@ export class EpochCache {
       // In Lodestar it usually means a list of validator indices of participants in a committee
       // In the spec it means a list of committee indices according to committeeBits
       // This `committeeIndices` refers to the latter
+      // TODO Electra: resolve the naming conflicts
       const committeeIndices = committeeBits.getTrueBitIndexes();
 
       const validatorIndices = this.getBeaconCommittees(data.slot, committeeIndices);
 
-      const attestingIndices = new Set(aggregationBits.intersectValues(validatorIndices));
-
-      return Array.from(attestingIndices);
+      return aggregationBits.intersectValues(validatorIndices);
     }
   }
 
diff --git a/packages/state-transition/src/signatureSets/indexedAttestation.ts b/packages/state-transition/src/signatureSets/indexedAttestation.ts
index 724b186bee40..cb4706c645fe 100644
--- a/packages/state-transition/src/signatureSets/indexedAttestation.ts
+++ b/packages/state-transition/src/signatureSets/indexedAttestation.ts
@@ -41,6 +41,7 @@ export function getAttestationsSignatureSets(
   state: CachedBeaconStateAllForks,
   signedBlock: allForks.SignedBeaconBlock
 ): ISignatureSet[] {
+  // TODO: figure how to get attesting indices of an attestation once per block processing
   return signedBlock.message.body.attestations.map((attestation) =>
     getIndexedAttestationSignatureSet(
       state,