The FBI ended its search of a California lake for a computer hard drive belonging to the suspects involved in the San Bernardino attacks this month, an official said Sunday. Investigators suspected that the shooters, who were inspired by the Islamic State group, also known as ISIS, dumped evidence linked to the shooting.

The search of Seccombe Lake, in a public park about 2.5 miles north of the Inland Regional Center where the shooting occurred on Dec. 2, began Thursday after reports surfaced that the suspects visited the park either before or after the attack. Authorities searched the lake for three days and recovered some objects.

"We have not commented on the items, or whether they are case-related, due to the ongoing investigation," FBI spokeswoman Laura Eimiller said Sunday, while responding to reports that the objects were not linked to the investigation, according to Reuters. "Divers tend to find all sorts of items in public lakes," she said, adding that any objects found "will be analyzed for evidentiary value in this case."

Investigators are working to piece together evidence found so far to determine what caused the suspects to go on a shooting rampage. Syed Rizwan Farook and wife Tashfeen Malik -- armed with assault rifles and guns -- opened fire at the social service center, killing 14 people and injuring 20 others. The couple was killed during a standoff with police nearly four hours after the attack.

Authorities are using surveillance footage to track the actions of the suspects in the time between the shooting and their deaths, a local media report said.

According to a local report, Jennifer Calderon, manager of the Circle K convenience store at the Valero gas station at Third Street and Waterman Avenue, said police told her the day after the attack that the shooters went inside the store 40 minutes after the attack. Police scrutinized video from inside the market, Calderon said, adding that the outside cameras were not functional.

However, San Bernardino police did not immediately confirm Calderon’s statement that the shooters entered the store.

Authorities have described Farook and Malik as “self-radicalized” and voicing support for ISIS. Investigators told the Los Angeles Times Saturday that one or both of the attackers were probably in direct contact with foreign terror groups.

According to federal government sources, investigators believe that the couple was planning an even bigger attack, the Los Angeles Times reported, adding that they were in the final planning stages of the assault on a location or building that housed more people. Investigators have based that conclusion on evidence on the couple’s computers and digital devices, one of the sources reportedly said.