WASHINGTON — Important clues about what drove Adam­ Lanza to mass murder probably sit on the computer the reclusive, technically minded 20-year-old used as one of his main contacts with the world, authorities said.

Lanza attempted to destroy his computer’s hard drive, the device that stores and retrieves data, before the killing rampage in Newtown, Conn. Police have declined to provide information on damage to the drive, but investigators remain hopeful that it can be repaired. Specialists, however, said any effort to recover data may be thwarted if the drive’s magnetic platters are shattered. If the damage is less severe, or if there are multiple platters, investigators may be able to glean information. Such efforts are slow and costly.