Simon Harwood, who admitted knocking Ian Tomlinson down with his baton, still faces an internal hearing, The Independent reported. Tomlinson's family is also expected to file a civil suit.
Jurors spent four days deliberating before finding Harwood not guilty. They were not told that Harwood had 10 disciplinary complaints on his record.
In 2001, Harwood avoided a hearing on a road-rage incident by leaving the Metropolitan Police on health grounds. He worked for the police as a civilian and then joined the Surrey Police in 2003 before returning to London where he was trained as a crowd-control officer during demonstrations and riots.
Tomlinson, 47, who had a longtime alcohol problem, was trying to get to the shelter where he was living when he got caught up in the protests in April 2009. He was helped to his feet after Harwood struck him but collapsed nearby and died less than an hour later of internal injuries.
Harwood's defense was that his conduct was justifiable given the situation.
"In April 2009, we saw the shocking video of Ian being violently assaulted by PC Harwood, just minutes before he died," Paul King, Tomlinson's stepson, said. "After the unlawful killing verdict at the inquest, we were expecting to hear a guilty verdict. It really hurts. But it's not the end, we're not giving up on justice for Ian. It's been very hard to keep going."