The man then left alone

footage shows Miller going into his apartment with a man on Monday night about 6.30pm

The global head of Citigroup's environmental and social risk management was found dead in his New York apartment on Tuesday with a laceration to the throat and investigators said late Wednesday it was a suicide.

Gruesome: Citigroup managing director Shawn D. Miller was found with his throat slit in his Manhattan apartment on Tuesday

The body of Shawn D. Miller was discovered in the bathtub of his condo in Manhattan's Financial District and police initially believed a third-party was responsible after finding no weapon.

However, after moving the 42-year-old, police discovered a knife beneath his body in the bathtub, the New York Daily News reports.

Investigators had been trying to find a man with whom Miller was seen walking into the apartment at 120 Greenwich St at about 6.30pm Monday night.

The man later left alone.

There were no signs of forced entry.

A doorman then made the gruesome discovery of Miller's about 3pm Tuesday.

It is believed a worried friend called the building - located near Albany St street and the September 11 Memorial and Museum - and asked if the doorman could check on Miller.

The doorman said the caller identified themself as Miller's Canadian boyfriend, according to The Post.

The banker was pronounced dead at the scene.

A medical examiner will determine the official cause of death.

Police said Wednesday they found drug and alcohol in the apartment, including what they believed to be crystal meth.

Investigators say Miller had hooked up with a stranger for sex Monday using the website backpage.com.

Citigroup acknowledged the death of the managing director in a statement sent out Wednesday.

'We are deeply saddened by this news and our thoughts are with Shawn’s family at this time,' Citigroup said in the statement to Business Insider.

Miller was a managing director for Citigroup's environmental and social risk management team.

According to his profile on LinkedIn, he has been with the company since 2004.

He worked on sustainability matters, including mining and renewable energy policies.

Scene: The doorman of Miller's building at 120 Greenwich St in downtown Manhattan found his body around 3pm on Tuesday

Miller oversaw environment policies that were implemented in over 100 countries.

The page described him as 'a thought leader and pioneer in sustainable finance focused on creating change and building sustainable business through collaboration, engagement and partnership with others'.

He formerly worked for the World Bank Group's International Finance Corporation

Miller graduated from Syracuse University in New York in 1995.