There were tears in the public gallery as 17-year-old Cairo Parker's manslaughter verdict was read out as someone cried out, "He's only a baby!"
The judge Mr Justice John Griffith Williams lifted restrictions on naming Parker and said he would hear mitigation tomorrow afternoon before sentencing the defendants on Wednesday morning.
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Police and coastguard discovered the bodies of 42-year-old Cheryl Tompsett and her five-year-old son Leo Tompsett on Monday.
It follows a similar move by ministers in Scotland.
A "small number of people" have been treated following a "reported minor explosion" at Southgate tube station in London, police said.