Friends notified authorities after finding a couple dead inside their California home on April 24 with the message, "Sorry, my first kill was clumsy," written in ink nearby.
Officials are now investigating the murders of engineer Golam and his wife, accountant Shamima Rabbi, and gaging motives, KGO-TV reports.
Their sons, aged 17 and 21, were not at the San Jose home at the time and were unharmed.
Police say the couple was shot at least once, but they have no further information about the murders and suspects beyond that.
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"I was shocked this is a quiet neighborhood,” neighbor Ben Mendoza said, reports KNTV. “We've been here 16 and 17 years so to hear this happened is really shocking."
The couple’s friends say they grew worried about the couple after not hearing from them for days.
Determined to find out what was wrong, they entered the home through an unlocked sliding glass door where they found their friends’ bodies lying on the hardwood floor.
Those who knew the Rabbis say the Muslim couple left Bangladesh decades ago and described them as humble, polite and peaceful people.
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"So that's why it's so difficult to reconcile to the tragic, violent end to such simple, gentle souls," Evergreen Islamic Center member Hasan Rahim said.
"We are surprised that they are no longer with us and especially going away in such a manner is something we just can't come to grips with," Evergreen Islamic Center member Faisal Yazadi added.
Meanwhile, the South Bay Islamic Association expressed its condolences while also asking fellow Muslims to forgive the murderers.
"The circumstances of their passing are still under investigation and therefore details of the Janaza/Burial are yet to be announced," the message said. "We ask Allah to forgive the deceased, shower His mercy on them, and make their graves a garden from paradise. In addition, we extend our deepest condolences to the family and ask Allah to grant them strength and patience during this most difficult time."
Police ask anybody with information to come forward.