OAKLAND -- A 42-year-old man was in critical condition Tuesday after he was shot multiple times when he answered the door to his West Oakland apartment, police said.

Police believe the gunman was trying to shoot someone else they thought was in the apartment but who was not there.

The shooting happened about 1:30 a.m. Tuesday in the 700 block of Adeline Street in the Acorn development.

Police said someone knocked on the apartment door and the man answered it. He apparently saw a man with a gun and shut the door but the shooter fired several rounds through the door hitting the man multiple times, police said.

The gunman fled on foot. The man was taken to a hospital where he underwent surgery.

Police believe the shooting was gang-related.

Police were also investigating whether another shooting in the same area Monday night was related to the Tuesday shooting.

Police said two suspects shot at four people about 9 p.m. Monday who were walking in the 1000 block of Eighth Street that is also part of the Acorn complex.

None of the people shot at were hit by gunfire and the suspects fled on foot.

Police believe the shooting is also gang-related.

Police and Crime Stoppers of Oakland are offering up to $5,000 in reward money in each of the shootings for information leading to the arrest of the shooters. Anyone with information may call police at 510-238-3326 or 510-238-3426 or Crime Stoppers at 510-777-8572.