A man and a woman have been arrested on suspicion of child abandonment after a newborn girl was found in a holdall on a doorstep in Reading.
A man aged 26 and a woman aged 18 were arrested in Winchester and are in police custody.
A note written in Polish was left with the baby who was dumped opposite the Polish Centre in London Road, Reading, on May 3, Thames Valley Police said.
The infant, believed to be between two and three weeks old, is in foster care after she was taken to the Royal Berkshire Hospital.
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Police believe it is a "distinct possibility" that Halliwell was a serial killer, beyond the two murders he was convicted for.
Tuesday's weather for the west of the region
Tuesday's weather for the east of the region