Following that, the officer stormed into a supermarket brandishing a pistol, and started shooting, instantly killing a guard and a saleswoman.

Customers had to dive for cover, but still five were wounded. The wounded have been taken to hospitals where some are said to be in critical condition.

Police patrols that arrived on the scene to strike the shooter down were drawn into a full scale gun battle with the distraught officer, with the gunman having several spare ammunition clips with him.

“He was shooting back fiercely. It’s a miracle that no one arresting him got hurt,” a police officer told the ITAR-TASS news agency.

“Yes, he is a police officer and unfortunately, he is the chief of the police department of ‘Tsaritsyno’ district,” said Vladimir Pronin, the Head of Moscow police.

Moscow police say the man was involved in a family dispute shortly before he began his killing spree.

'A decent officer with a brilliant future'

Denis Yevsyukov

”He was at the helm of a criminal police department before taking on the Tsaritsino district. He was a decent officer with a brilliant future,” one of Yevsyukov’s colleagues told Gazeta.ru. He added that "nothing spoke about his possible psychiatric disorder."

However, another of Yevsyukov’s colleagues stated that before the accident, Evsyukov "had been weird, nervous and impulsive."

A Moscow court has issued an arrest warrant. Yevsyukov is suspected of murder, attempted murder, and arms trafficking. Now he is expected to undergo psychological checks.

Police had been ‘looking for’ murder weapon for 9 years

Experts have already verified that the pistol the major used for the killings was not his service pistol, but rather, was earlier stolen in Chechnya, and has a criminal record.

Locals are shocked by the incident, as are police officials investigating the case.

“Last night Yevsyukov was celebrating his birthday in a restaurant. He had an argument with his wife there,” stated Investigation Committee spokesman Vladimir Markin.

“When he returned home, the police officer put on his uniform coat over his civilian clothes and left. And then the incident happened. The investigation has discovered that Evsyukov did not use his service gun, but another weapon we've been looking for for 9 years.”

Control over officers should be tightened – experts

Experts say that in general, control over police officers who have access to weapons, should be intensified many times over.

“Firstly, there should be control over the mental state of those who are carrying weapons,” says psychiatrist Mikhail Vinogradov.

“Secondly, it's crucial to have annual medical examinations, including both psychologists and psychiatrists. Such mental states always have a background. Slowly anger, irritation and depression, get stored for a long time, and then we have an explosion.”

In turn, a police source has unofficially informed Interfax news agency that starting on Monday, the Moscow Police Department is preparing to conduct an all-out examination of all service guns and ammunition of law enforcement officers.

Total psychologic and psychiatric tests of all weapons-bearing personnel are also expected.