A schizophrenic who stabbed to death a mother in her own home in Hertfordshire as she tried to stop him kidnapping her two young children has been given an indefinite hospital order.

Nicola Cross was knifed 10 times by Marcin Porczynski after the 24-year-old broke into her house in Hemel Hempstead on September 14 last year.

Mrs Cross, 37, rang her husband Daniel in panic and he was forced to listen helplessly as she pleaded with the killer - a complete stranger - before hearing her scream loudly and the line fall silent.

Nicola Cross was knifed 10 times by Marcin Porczynski.

After Porczynski pleaded guilty to manslaughter on grounds of diminished responsibility on Friday, Mr Cross, who was away on business at the time of the attack, said in a statement the horrific phone call "plays over and over in my head", adding: "I will never forgive myself for not being there to protect her."

The Polish national, who had denied murder, was sentenced at St Albans Crown Court on Monday by Judge Andrew Bright QC, who said the "horrific and senseless killing" represented "the worst possible nightmare of every husband and parent".

He said: "Although Nicola Cross tried to reason with you and heroically did her best to protect herself and her two young children from you, she was completely defenceless against the vicious knife attack you then launched upon her."

Ordering Porczynski to be detained at a mental hospital, the judge told him he would only be released when deemed no longer a danger.

He added: "You have devastated the lives of the Cross family and left two young children to grow up without the wonderful mother who so loved and cared for them.

"Those responsible for deciding if and when you should ever be released back into the community will need to look long and hard at the full circumstances of the dreadful killing which your mental illness led you to commit."

Porczynski wept in the dock on Friday as he heard Mr Cross describe how he could see "no future happiness, no end to this trauma until my life comes to an end".

The court heard that he had been suffering from paranoid schizophrenia, hearing voices telling him to "free" children who were being mistreated or risk harm to his own family.

Mrs Cross was fatally wounded as she tried to stop him from getting to her children as they slept.

Prosecutor Chris Donnellan told the court Porczynski had been seen roaming the neighbourhood in the Hertfordshire town in the hours before the attack, knocking on doors and asking if there were children there.

Mrs Cross called the police shortly before 11pm after Porczynski, who lived nearby, began peering through the windows of her house on Dunlin Road.

Officers who stopped him found he was a "bit distant", and he was allowed to return to his home on nearby Claymore Avenue. But he returned to the area at around 11.30pm - this time armed with a small knife.

At first he broke into a neighbouring address by accident and, while police responded to the reports of a burglary, officers heard a smash and screams from next door.

After breaking through the patio doors of Mrs Cross's home, Porczynski grabbed a larger knife from the kitchen and climbed the stairs.

Mr Donnellan said it appeared he initially used the smaller knife for the attack before discarding it in favour of the large one.

Porczynski then went up to a bedroom and laid down the bloody knife before trying to carry the children away, but he did not physically harm them, the court heard.

A neighbour heard one of the children telling the attacker: "No, I don't want you here."

Officers then stopped the killer before he left the property, reporting that he appeared "vacant". They found the children at the bottom of the stairs, where one told them: "He has hurt my mummy badly."

The youngsters, who were said to be in a state of shock, were then kept in aroom upstairs as officers attended to Mrs Cross, who was declared dead at the scene.

The court heard that the defendant had started behaving abnormally three weeks before he killed her, alarming a friend by frequently referring to fictitious events.

After his arrest Porczynski claimed he believed he had to save the children, who were being "starved". Traces of cocaine and cannabis were found in his blood but the prosecution said bore no bearing on the attack.

Four further charges of attempted kidnap, burglary and aggravated burglary were ordered to lie on file.