Four people, including a police officer, were killed and about 40 others were wounded Wednesday in a terrorist attack at Britain’s Parliament that sent crowds running for their lives before police shot and killed the attacker.

Police for several hours said the attacker had killed three people. Acting Deputy Metropolitan Police Commissioner Mark Rowley said Wednesday night that a fourth victim had died.

The victims included London Metropolitan Police Constable Keith Palmer, 48, a 15-year veteran who was a husband and a father, Rowley said. Palmer was stabbed at the House of Commons and died despite the efforts of doctors and a passing government minister to save him.