Chao had been sacked by Mount Sinai almost a decade ago over 'research misconduct' and sued twice

Dennis Charney, dean of New York's Mount Sinai school of medicine, was shot at 7am in Chappaqua, New York, Monday, and left severely wounded

A medical researcher who was at the forefront of gene therapy for hemophilia allegedly opened fire at one of the country's most senior doctors at Bill and Hillary Clinton's favorite hometown deli, early on Monday.

Hengjun Chao is accused of firing fired a double-barrel shotgun at Dennis Charney, dean of Mount Sinai school of medicine in New York, as the doctor left Lange's Little Shop and Delicatessen.

A man delivering cold cuts was also hit by the blast.

It is less than a mile from the Clinton family home in Chappaqua, New York, and one of Bill and Hillary's favorite local shops.

Chao, 49, then calmly put the gun back in the trunk of his car, parked in a Walgreens parking lot and waited for cops to arrive, local police chief Charles Ferry said.

Wounded: Dr Dennis Charney, who was seen with Martha Stewart at the opening of the Center for Living at Mount Sinai hospital in New York, was badly wounded in the shooting at the deli

Accused: Alleged shooter Hengjun Chao appeared in court on Monday afternoon (right) after the 7am shooting in Chappaqua. He had a distinguished medical research career (left)

Two people were shot outside Lange's deli in Chappaqua, New York on Monday

Damage: Police said the shooter had used buckshot to open fire on his former boss

The attack happened at 7 am on Monday as Chao's former boss left Lange's, a favorite spot of both Bill and Hillary Clinton.

Chao had traveled to Chappaqua from his home in the village of Tuckahoe, New York, then lay in wait, cops believe.

As his ex-boss left the deli, he opened fire. 'There were only one or two shots, not the nine that has been reported,' said Ferry.

'When buckshot gets fired it spreads out.'

Chao made no attempt to flee the scene, said Ferry, and was taken into custody without incident. He is cooperating in the investigation.

Chao appeared in court on Monday night where he was charged with one count of attempted second degree murder.

He was wearing a hooded white jumpsuit with his hands shackled at the waist. He was remanded in custody with defense attorney Michael Rubin making no application for bail.

Chao will next appear in court on September 7. Town judge Noah Sorkin ordered that Chao should have stay away from Charney, who lives in Chappaqua, for one year.

Dr Charney, who as the Mount Sinai dean was Chao's ultimate boss is still receiving treatment at the Westchester Medical Center in Valhalla, New York. The second man has been released.

Ferry said the dispute went back some time. 'I don't know the exact year but it wasn't recent.

'It would seem to be an act of revenge,' he said. 'It is possibly anger towards one of the victims.'

Chelsea, Hillary and Bill Clinton are regular visitors to the deli, seen here in 2000

Family favorite: Bill Clinton visited the deli on his first full day as a private citizen after completing his eight years in office in 2001

The street outside the deli was closed off on Monday. A neighbor said he saw 'at least eight or nine bullet holes' in the door frame of the store

The deli is just down the road from the Clintons' house on a leafy street. They bought the residence in 1999

Ferry said detectives hope surveillance video from the Walgreens store will help them piece together exactly how long Chao was waiting for his victim to leave Lange's.

Charney is one of the country's leading doctors. As well as being dean of Mount Sinai's medical school, he is a professor of psychiatry, neuroscience and pharmacology and systems therapeutics at the school.

His primary work has been in psychiatry, and has seen him develop medical treatments for schizophrenia and depression.

He holds a string of awards for his work and has also been involved in research post-traumatic disorder in veterans.

Chao, who was educated at Peking Union Medical College, in Beijing, China, had been a pioneer of gene-based therapy for both hemophilia, a condition in which the blood does not clot properly, and muscular dystrophy, which causes muscle wasting.

In 2002, when he was a researcher at the University of North Carolina, he told BBC News that work he was involved in which had led to some mice being cured of hemophilia through their genes being altered could lead to an effective treatment for people with the condition.

The treatment used 'gene-splicing', where faulty genes which cause disorders such as hemophilia are injected with corrected genetic material. Such treatments are at the cutting edge of medicine, but none has yet proved a complete breakthrough.

So far only one gene therapy is licensed for use in the U.S. and Europe, a therapy for a rare form of pancreatitis.

However he was involved in a legal dispute with Mount Sinai hospital and school of medicine in New York in 2010.

The Chappaqua, NY residence is where Hillary and Bill moved into after leaving the White House

It is unclear if Dr Charney was directly involved in the dispute, but as its dean was in overall charge of medical training there when Chao sued.

He had been an assistant professor when he sued, alleging racial discrimination, after being sacked for what the school described as research misconduct.

Neighbor Richard Meyer said he heard shots fired in the attack. 'You just don't expect this in Chappaqua,' he said.

The school fired him after a lengthy investigation found that he had committed 'research misconduct.'

According to papers filed in federal appeals court, Chao, who had worked at Mt. Sinai since 2002, lost the case, because he could not prove that the 'rigorously-investigated charge and finding' that he had 'committed research misconduct and violated professional or ethical standards,' was a pretext for firing him because of his race.

He lost the case and an appeal, but in 2013, it was announced he would work with a foundation dedicated to treatment of another blood disorder, blackfan diamond anemia.

It said that it would build on gene-splicing technology developed by Dr Chao. His current employment status could not be verified.

Neighbor Richard Meyer said earlier that he was working on his computer when he heard shots ring out.

When he went up to Lange's he saw 'at least eight or nine bullet holes' in the doorframe.

'There were three holes in the left hand door, three above the handle of the right glass door, one above the receptacle for cigarette butts and another on the right side of the door,' Meyer, 72, told DailyMail.com.

Meyer said by the time he got out police were already on the scene.

'You just don't expect this in Chappaqua,' he added.

'I was talking to someone in the parking lot who was asking what happened and I said a shooting. She said what movie? She would never think there could have been a real shooting here.'

Clinton leaving a fundraiser on Sunday as she continues along the campaign trail

The shooting happened less than a mile from where the Clintons have their family home.

Bill Clinton visited the deli on his first full day as a private citizen after completing his eight years in office.

Lange's owner said in 2014 that Bill sometimes comes in as often as twice a week, while Hillary stops by slightly less often.

The Clintons bought their house in the neighborhood in 1999, towards the end of their second term in the White House.

It was reported at the time that they chose the 11-room, 5,200-square-foot Dutch colonial house to help the then First Lady with her tilt at New York's Senate position, for which she required legal residency in the area.