Mum created over 300 fake Instagram accounts to stalk and abuse

A US fitness trainer has been sentenced to five years in prison for creating fake Instagram accounts to stalk her ex-business partner.

The FBI claims Tammy Steffen created 369 Instagram accounts and 18 different email addresses in order to send threats and abuse to her ex-business partner, as well as competitors in bodybuilding.

According to the Washington Post, messages written by the mother of four included "I plan to slice you up into little pieces" and "Your blood shall I taste."

Steffen, 37, has pleaded guilty to federal charges of cyberstalking and sending threatening communications online.

FBI special agent Kristin Rehler told WFLA the "extent of her crime is astounding".

Steffen's cyberstalking targeted five victims in three states.

Authorities say the mum also used a headless baby doll and a fake kidnapping scheme to try to extract revenge on her former business partner.

It emerged that Steffen felt her ex-business partner has sabotaged her chances of winning an online fitness competition, which authorities say is untrue.

She then began to call authorities, claiming she was being threatened and that someone had tried to kidnap her 12-year-old daughter, blaming her former business partner for the attempt.

Authorities were able to prove Steffen had staged the ordeal and forced her own daughter to urinate on herself to make the story more believable.

The fitness trainer was arrested on July 17 on charges of filing a false police report, tampering with evidence and child neglect.

A witness tampering charge was added days later when she called her daughter from jail and told her to claim the kidnapping plot was her doing.

As police investigated the kidnapping plot, they uncovered the rest of Steffen's abuse and threats against others.