The Naval Criminal Investigative Service has not ruled out the possibility of a connection between the large blaze that severely damaged the USS Miami, a small fire that later broke out near the submarine and a fire alarm that was pulled.

NCIS spokesman Ed Buice said that while the ongoing investigation has not found evidence that suggests the three incidents are related, "that possibility cannot be eliminated at this time."

The Groton-based Miami (SSN 755) was in a dry dock at the Portsmouth Naval Shipyard for maintenance and upgrades when it caught fire at 5:41 p.m. May 23 and burned until 3:30 a.m. the next day.

The fire, which caused more than $400 million in damages, started in a vacuum cleaner used to clean the work site at the end of a shift, preliminary findings show.

NCIS is offering a $5,000 reward for information about either the small fire outside the Miami in the dry dock at about 7 p.m. on June 16 or the fire alarm that was pulled in the same general vicinity at about 11 p.m. June 19. The June 16 fire was immediately extinguished with a hand-held fire extinguisher.

"The goal of the ongoing investigations into the USS Miami fire is to determine conclusively how and why it occurred and to be able to prove that there was - or just as importantly that there was not - any intentional wrongdoing or criminal activity," Buice said in a statement Thursday.

Buice said he could not discuss any additional details about the investigation.

The Navy has asked Congress to add $220 million to the operations and maintenance budget for emergent and unfunded ship repairs, which will be used to continue the repairs on the Miami. The Navy is also investigating options to pay for the additional repair costs once it receives funding from the 2013 fiscal year spending bill, according Lt. Courtney Hillson, a Navy spokeswoman.

Extensive engineering assessments are still ongoing to determine the full cost to restore the submarine, Hillson added, and cost estimates will continue to be refined as more data is gathered.

NCIS launched a new hotline last year to receive anonymous crime tips via text or an online form. To submit a tip, visit www.ncis.navy.mil/contactus/pages/reportacrime.aspx.

j.mcdermott@theday.com