* Aid worker believed to have been held by al Shabaab
* Critics denounce her decision to convert to Islam
By Emilio Parodi
MILAN, May 12 (Reuters) - An Italian aid worker, freed at the weekend after being held hostage for 18 months by Islamist militants in Africa, has been deluged with hate mail because she converted to Islam, judicial sources said on Tuesday.
Magistrates have opened an investigation into the abuse to see if charges of aggravated criminal threat can be laid against some of the senders, the sources said.
Silvia Romano was working as a volunteer in an orphanage in a village in southeast Kenya when she was seized by gunmen in November 2018. She was quickly smuggled across the border into neighbouring Somalia, where she was believed to have been detained by the Islamist group al Shabaab.
Romano, 24, was greeted by the prime minister and foreign minister when she arrived back by plane on Sunday, smiling broadly and wearing a hooded garment that covered her hair.
Although she has not spoken in public about her ordeal, her family have confirmed that she converted to Islam during her imprisonment and has changed her name to Aisha.
Newspapers quoted her as telling officials that she had chosen to become a Muslim of her own free will after reading the Koran and had not been abused by her captors. However, reports of her conversion sparked fury in some circles.
“Islamic and happy. Silvia the ungrateful,” said the front-page headline of right-wing daily Il Giornale on Monday. (Writing by Crispian Balmer; Editing by Giles Elgood)