What does Acts 5:22 mean?

The chief priests have arrested the apostles for teaching the people that Jesus rose from the dead. The next morning, as the whole council prepares to question them, the prison is empty (Acts 5:17–21). It's possible the guards are reminded of the empty tomb (Matthew 28:11–15).

The chief priests, elders, and scribes of both the Sadducees and the Pharisees worked diligently to get Jesus arrested and executed. They bribed one of Jesus' followers to arrange a quiet time for the arrest (Matthew 26:14–16, 47). They sought men who would lie under oath that Jesus had broken the Mosaic law, despite the fact that false testimony about a capital offense was, itself, a capital offense (Matthew 26:59–60). They manipulated the Roman governor to do the killing, blackmailing him with the accusation that to do otherwise would mean he was committing treason against Caesar (John 19:12). And they incited a crowd to force Pilate to release an insurrectionist instead of the innocent Jesus (Matthew 27:20).

After the deed was done and Jesus was buried, they even asked Pilate to officially seal and guard the tomb so the disciples couldn't steal His body (Matthew 27:62–66). So when the guards came to the chief priests with the message that angels had appeared to roll the stone away and the tomb was empty, the priests had nothing. They bribed the soldiers to claim the disciples stole the body—but didn't formally charge the accused grave robbers—and tried to pretend it would all go away (Matthew 28:11–15).

Now, those same disciples are teaching that Jesus has risen from the dead and belief in Him will reconcile the people to God. There is no talk of sacrifices or offerings in the temple, as the priests would prefer. The priests had the apostles arrested, and now, their prison cells are empty. And the officers have to tell the priests.