If they say, "Come along with us; let's lie in wait for innocent blood, let's ambush some harmless soul;" (NIV)
If they say, Come with us; let us lie in wait [to shed] blood, let us ambush the innocent without cause [and show that his piety is in vain] (AMP)
If they say, Come with us, let us lay wait for blood, let us lurk privily for the innocent without cause: (KJV)