Twelve minutes was all that police had when they received an anonymous tip-off that their prime suspect wanted for stabbing an officer was about to fly out of Hong Kong on a Cathay Pacific flight bound for London just before midnight on Wednesday.

“It was lucky. Without the anonymous call, the suspect could have fled Hong Kong,” a police source told the Post.

The call was received at 11.43pm by a police inspector at Hong Kong International Airport. The informant used a paid SIM card to let police know that the man they had been hunting across the city for the past eight hours was about to take off at 11.55pm, and then hung up immediately.

With precious seconds ticking away, police made a frantic dash to the boarding gate and plain-clothes officers boarded the aircraft to look for the 24-year-old suspect, surnamed Wong.

He was not in his designated seat and did not respond to aircrew calling out his name. A sweep of the plane soon found him sitting in the row in front of his own seat.

“They seized his backpack and found about HK$40,000 in local and foreign currency along with his expired BN(O) passport,” the source said.

He had apparently used a valid Hong Kong SAR passport to go through immigration and final checks by airline staff.

Events were set off hours earlier and miles away on Hong Kong Island, at around 4pm, when a policeman chasing after a protester during a defiant backlash against the new national security law imposed on the city by Beijing became separated from his colleagues. He was set upon by a violent mob.

The policeman was stabbed in the shoulder and left bleeding on the ground while his assailants, including the primary attacker, fled the scene on Causeway Road, near Hing Fat Street, Tin Hau.

“While the bystanders offered no helping hand, suspects fled. Police express the strongest condemnation against such a violent act,” the force said in a Twitter post.

The policeman, who was among seven officers injured in Wednesday’s protest violence, said in a Weibo post that although he was still in pain, his condition had improved after surgery, and he had no regrets about doing his duty that afternoon.

“Although I am injured, there are still 30,000 officers to arrest the rioters for me, for Hong Kong and for the country,” he said.

Police took the suspect back to his home in Tsz Ching Estate in Wong Tai Sin for a search on Thursday night.

Video footage of the attack was shared widely online, along with still images zooming in on the masked attacker as Hong Kong’s intrepid internet users tried to identify him unofficially.

Former chief executive Leung Chun-ying had offered a reward of HK$500,000 for information leading to his arrest.

In an interview with local media, the man’s father denied speculation online that his own family had turned him over to police. He also mentioned that his son was a civil engineer.