A man suspected of taking part in the kidnapping of a British human rights worker and her parents in Gaza has been arrested, Palestinian officials say.
The captors released a video shortly before freeing the family
The arrested man led a faction of the al-Aqsa Martyrs' Brigade, the militant arm of the Fatah movement, police said.
Kate Burton was freed with her parents last week, two days after being abducted in the southern town of Rafah.
Abductions and clashes between armed groups have spiralled in Gaza since an Israeli withdrawal last year.
But arrests remain rare because of the lack of law and order, reports BBC Gaza correspondent, Alan Johnston.
A Palestinian security official told the AFP news agency al-Aqsa faction leader Alaa al-Hams had been arrested on suspicion of being "behind the kidnapping of the British aid worker and her parents".
Friends and relatives of Mr Hams fired weapons into the air to protest at the arrest in Rafah.
They later stormed the local office of the Palestinian interior ministry.
'Nervous and angry'
Ms Burton, 24, her father Hugh, 73, and mother Helen, 55 - known as Win - of Newbury, Berkshire, were abducted when their car was intercepted by masked gunmen.
The human rights worker - who has vowed to continue her work in the Middle East - has denied claims she did not help the investigation into the identity of the gunmen.
And in a BBC interview she said she felt guilty about putting her parents at risk but did not regret taking them to see the "positive side of the Palestinians".
She said of their time in captivity that she had initially remained calm but became "nervous and angry" as promises to release them were not acted upon.
Shortly before their release a previously unknown group, the Mujahideen Brigades, released a video showing Ms Burton with a masked gunman who said the three hostages were being freed in a gesture of good faith.
However, the gunman urged the UK to exert more pressure on Israel or risk further kidnappings - particularly of international observers due to oversee elections in Gaza later this month.