The investigation has revealed that the powder inside the envelopes contained a small amount of arsenic. The amount of arsenic could be up to 10%.

Arsenic is a naturally occurring compund that can be lethal to humans in larger proportions.

Exposure to arsenic, particularly through inhalation can lead to inflammation in the lungs, irritation in the nose or even bleeding.

Police used mass spectrometry and gas chromatography to identify the powder.

Earlier this week, multiple judges of the Lahore High Court had been sent suspicious letters containing threats and a suspicious powder. The letters had come soon after similar letters were sent to judges of the Islamabad High Court and Supreme Court.

It had been speculated that the powder might be arsenic, which has now been proven false.