The Secret Service on Thursday still had no suspects in the investigation into who brought cocaine into the White House over the weekend, and it's not clear whether a culprit will ever be found, a source told Fox News Digital.

The source, who is familiar with the Secret Service probe, told Fox News Digital on Thursday that it will take time to review the evidence and said officials admitted there is a possibility they will not be able to determine who brought the drugs into the White House on Sunday.

The source added that multiple tests have been run on the cocaine container, including DNA and fingerprints tests. 

The investigation is expected to be concluded early next week, and the source provided more detail on where exactly the drugs were found – in a phone cubby of an entrance off West Executive Avenue, which is in the lower-level West Wing lobby.

MEDIA JOKES ABOUT COCAINE FOUND IN WHITE HOUSE: WE NEED A 'BLOW BY BLOW' PROBE OF THIS

President Joe Biden

President Joe Biden meets with Swedish Prime Minister Ulf Kristersson in the Oval Office of the White House July 5, 2023, in Washington, D.C. (Drew Angerer/Getty Images)

The location is not a place where heads of state usually come through and is usually an entrance the vice president, cabinet secretaries, White House staff and others use, according to the source.

The area is not open to public visitors except for those receiving special tours by White House staff. White House staff use it when they travel between the West Wing and the Eisenhower Executive Office Building, which is across the non-public West Executive Avenue.

The source also told Fox News Digital that the Secret Service has received the letter sent by Republican Sen. Tom Cotton demanding answers on how the drugs made it into the White House and that they plan to respond to him.

On Wednesday, the Secret Service confirmed to Fox News that the substance found in a bag in the West Wing of the White House by a member of the Secret Service on Sunday evening was cocaine. The discovery prompted the response of a hazmat team and the fire department while the Secret Service blocked the streets around the White House.

TRUMP ATTACKS BIDENS, MEDIA FOLLOWING DISCOVERY OF COCAINE AT WHITE HOUSE OVER THE WEEKEND

White House Press Secretary Karine Jean-Pierre was peppered with questions from reporters Wednesday but declined to provide details on the matter and deferred to the ongoing investigation. She also pointed out that President Biden and his son Hunter were at Camp David from Friday until Tuesday.

"As you know, the President and the First Lady and their family were not here this weekend, as you all reported on this and as you also know that they left on Friday and returned just yesterday," Jean-Pierre said. "Where this was discovered is a heavily-traveled area where many White House, West Wing, I should be even more specific, West Wing visitors come through this particular area. I just don't have anything more to share."

CLICK HERE TO GET THE FOX NEWS APP 

Karine Jean-Pierre at briefing

White House Press Secretary Karine Jean-Pierre was pressed by reporters about the cocaine that was allegedly found in the West Wing over the weekend. (Drew Angerer/Getty Images)

While federal investigators have yet to determine who brought the illegal narcotics into the White House, internet bookies have identified President Biden's son Hunter as the most likely candidate. 

Hunter, a recovering crack addict, has been given +170 odds as being the culprit by Overseas sportsbook BetOnline.ag. The site lists other potential candidates, many of which appear to be jokes such as Kansas City Chiefs tight end Travis Kelce who recently visited the White House.