Police say a homeless man has confessed to stabbing three people in two separate attacks in Manhattan over a 12-hour period, and now investigators are trying to link him to a third stabbing incident that took place in the same time period.

According to NYPD investigators, 21-year-old Kenny Alexis admitted to stabbing two Canadian tourists around 4 a.m. Wednesday in Duffy Square. Investigators say Alexis also admitted to stabbing a tourist from Texas on a southbound C train during Tuesday evening's rush.

Alexis was arrested at a McDonald's following the attack on the Canadian victims. Both of them had to be hospitalized, though one has already been released.

The victim in the C train stabbing, 21-year-old Christopher McCarthy of Houston, is still listed in critical condition.

Police Commissioner Ray Kelly said McCarthy didn't even realize he'd been stabbed at first.

“He punches the victim in the chest. The victim thought that he was punched and not stabbed, until he looked down and saw blood on his garment," Kelly said at a news conference Wednesday.

Police still don't have a motive in the attacks.

Meanwhile, Alexis is also being questioned in connection with a stabbing at the Rockefeller Center subway station about an hour before the attack on the Canadian women. Ambrosio Castro, 30, was stabbed twice in the stomach.

Castro’s injuries are not believed to be life-threatening.

Alexis has not been formally charged with a crime, but he is being held by police. Charges against him are pending.

Meanwhile, Joseph McCarthy, the father of the C train stabbing victim, spoke to the media Wednesday at St. Luke's Hospital, where his son underwent surgery.

Holding back tears, McCarthy thanked doctors for the treatment they are giving Christopher, and said his son has already forgiven his attacker.

"My wife and I are very thankful for the immediate and necessary care that was provided to our son Chris after his random attack,” said McCarthy. “My son has forgiven his attacker and hopes that he can get help."

Doctors say the wound was deep enough to go past the breast bone and actually pierce McCarthy’s heart. They say, given the amount of blood that was in his chest, McCarthy's condition could have been worse.

“I would say he is extremely lucky, given the location of the injury and the fact that he had to travel a considerable distance before being evaluated,” said Chief Trauma Surgeon Dr. Raymond Wedderburn. “He certainly was extremely lucky."

Doctors say McCarthy is still in intensive care, but he is alert and talking.

His family says this incident would not stop them for visiting New York again.