Police investigating a deadly shooting in San Bernardino, California, searched a small lake visited by the suspects the day of the attack. FBI divers combed the waters of the Seccombe Lake Park, which is just two miles from the centre for the disabled where Syed Farook and his wife Tashfeen Malik killed 14 people on 2 December.

Authorities said agents took the plunge as they searched for evidence in connection with the gun rampage but did not specify what exactly they were looking for. "We have indications through leads that at some point they came to this park," said FBI spokesman David Bowdich. "There is no belief that there is anything dangerous at this place as a result of this incident."

Local media quoted security sources close to the probe as saying detectives were searching for electronic devices, including a hard drive that the shooters sought to destroy ahead of the massacre. Farook, 28 and Malik, 29, a married couple of Pakistani descent were killed in a shootout with police hours after the attack that targeted a Christmas party held by Farook's colleagues at the Inland Regional Center.

The incident is being investigated as an act of terrorism, as police believe the pair were moved by extreme Islamist views. Officials said both became radicalised some years ago. Malik reportedly pledged allegiance to Islamic State (Isis/Daesh) leader Abu Bakr al-Baghdadi on social media the morning of the shooting.

Earlier this week it emerged the couple who met online might have been planning the attack even before getting to know each other in person. Detectives said Farook, who lived in the US, and Malik, who used to reside in Saudi Arabia and Pakistan, already discussed martyrdom and jihad in 2013. Malik entered the US on a fiancée visa one year later.