The envelope businessman Martin Njoroge Nduati received from Barclays Bank containing a white powder looked substandard because it did not bear the bank's logo, he said.
However, another envelope inside the larger parcel was complete with the logo, and was self-addressed to the bank's Nairobi Area Manager.
After collecting the parcel at the General Post Office in Nyeri Town on Sunday evening, he discovered two days later that inside also lay a folder with the white powder.
"I opened the letter on Sunday, but ignored the folder contained there until Tuesday," he said.
On Tuesday, he sent an employee, Ms Jane Muthoni to take the parcel to the district public health officer, Mrs Pauline Ngare.
Since he never thought the parcel posed any threat, he did not take any precautions when handling it, he said.
Meanwhile, Jomo Kenyatta International Airport was put on "red alert" after the threat of bioterrorism became real.
However, the airport manager, Mr Yatich Kangugo, said Kenya Airports Authority could not explain the measures, citing security issues.
Yesterday morning, the airport's management met to discuss ways of dealing with the threat.
In another development, the United States Embassy promised to co-operate with Kenya authorities following the confirmed incident of anthrax delivery by mail.
A statement said the embassy's Federal Bureau Investigations (FBI) office had already examined the suspect materials.
The embassy said it had contacted FBI headquarters in Washington.
Meanwhile, private parcel companies stepped up security measures yesterday following the confirmation of anthrax threat in Kenya. DHL Worldwide Express said it usually does not accept any pre-sealed consignments from unknown shippers.
The company also insists on every shipper's identification and conducts random shipment inspection.
BKB Courier Services said their duty was to deliver mail and not to open it. "We handle it the way we have always done, an official said.
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