It started with a call for a welfare check around 12:30 p.m. for someone who reportedly lived alone at a home on The Strand near Beach Street and Sixth Street.
The Hermosa Beach Police Department said someone barricaded themselves inside the home when officers arrived and claimed they were armed.
That's when SWAT team and crisis negotiators were called to the scene.
The person ultimately surrendered and was detained after about seven hours. Officers then found a man, who has not been identified, dead inside the home.
It's still not clear how the person in custody and the person found dead are connected.