Mumbai Police's Crime Branch unit on Wednesday arrived in the national capital to question gangster Lawrence Bishnoi in connection with the threat letter to screenplay writer Salim Khan and his son and Bollywood actor Salman Khan, police said.

The Mumbai Police had recorded the statements of the father-son duo and also enhanced the security around the actor's residence in suburban Bandra. The police also took the statements of two bodyguards of Salim Khan.

According to a police source, the letter said, "Salim Khan, Salman Khan Bahot Jald Aapka Mooselwala Hoga G.B L.B... (Salim Khan, Salman Khan, very soon you will meet Moosewala's fate.)"

It is speculated that G. B. and L. B. may refer to gangsters Goldy Brar and Lawrence Bishnoi, though police has not made any statement on this aspect.

Punjabi singer Sidhu Moosewala was shot dead by unidentified assailants in Punjab's Mansa district on May 29.

"Gangster Lawrence Bishnoi is under the police remand of Delhi Police in connection with a case of Arms Act and will be produced before court on Friday. He was also questioned in connection with the killing of Punjabi singer Sidhu Moosewala. Though he did not reveal the names of his associates in the Moosewala killing, he accepted that he had fierce rivalry with the singer," a Delhi police official said on condition of anonymity.

"... now Mumbai Police's Crime branch has come to Delhi in connection with the threats issued to Salman Khan and his father Salim Khan. It a case pertaining to Mumbai Police so they along with our unit will jointly interrogate Bishnoi in the case," he added.

After Moosewala's killing, police had termed the incident as a case of an inter-gang rivalry. The Bishnoi gang was said to be behind the murder.

Canada-based Goldy Brar, who is a member of the Bishnoi gang, had claimed the responsibility for the murder.