Three other people were arrested in Tottenham, north London, at the same time as McLoughlin, police said.
The 54-year-old man from Tottenham, 45-year-old woman from Edmonton, north London, and 50-year-old man from Hackney were arrested on suspicion of assisting an offender.
All four are being questioned at Hatfield police station, Hertfordshire Police said.
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A woman died as she crossed the road when she was struck by four separate motorists who police believe did not stop.
Patrols including local volunteers have been set up after the grisly finds in Thamesmead in the last month.
Thieves targeted a property in Richmond on Monday afternoon.