After scouring a San Bernardino lake for clues into this month’s terror attack, divers have recovered some items, the FBI said Sunday, according to CNN.

However, the search turned up nothing related to the investigation, a law enforcement source told the network.

The federal agency initially declined to comment on whether the items are related to the mass shooting that left 14 people dead, but the law enforcement source said later the three-day search yielded nothing useful to the investigation.

The source declined to describe the items found.

Married couple Tashfeen Malik and Syed Farook  killed 14 people and wounded 21 others when they opened fire at participants of a holiday party hosted by Farook’s co-workers with the county health department on December 2.

Investigators are seeking the electronic trail of the killers and trying to find out whom they interacted with, how they hatched and carried out the plot, and why, according to CNN.

One of the items divers were likely looking for was a missing hard drive from the couple’s computer. Investigators believe the hard drive was removed as a way to hide information about the crime.

Though it does not appear the hard drive was found in the lake, investigators have another means of gathering data from the drive: Internet service providers can retrieve months of records of Internet activity linked to the IP address associated with the killers, the law enforcement source said.

FBI Director James Comey said last that the two may have married as a ploy to fool American immigration authorities, adding that Farook and Malik had discussed jihad and martyrdom even before they became engaged, meaning they were radicalized as early as the end of 2013.

Earlier this week,  the FBI said Farook and Malik were both radicalized “for quite some time” and hat taken target practice at Los Angeles-area shooting ranges, and once “within days” of the massacre.

It is believed Farook had contact with people from at least two terrorist organizations overseas, and investigators have also said Malik had pledged allegiance to the Islamic State (ISIS) group in a Facebook posting.

David Bowdich, the assistant director of the FBI’s Los Angeles office, would not comment on what the divers were looking for. But the lake is a few miles from San Bernardino’s Inland Regional Center, where the massacre occurred.

The killers were in the area “at some point,” he said, but he did not specify if it was before or after the massacre.