The blasts were part of the August 11-12 spate of arson and bomb attacks in seven tourist towns, which resulted in four people being killed and 35 injured.
The 21-year-old Muhammad denied charges of possessing war-grade explosives without permission, conspiring to commit arson and racketeering.
So far, arrest warrants have been issued for nine suspects.
Muhammad and Trang arson suspect Abdul-Kadae Salae are in custody.
The seven fugitives are: Phuket bomb suspects Ahama Lengha and Yusoh Maetimoh; Phang-Nga firebomb suspect Sukiman Kubaru; Nakhon Si Thammarat bombing suspect Hakeem Doloh; and Hua Hin bombing suspects Russaran Baima, Asmin Katemmadee and Seri Waemamu.

Targeted raids
Srivara also spoke at a press conference to announce the achievement of the police in the crime sweep and targeted searches between October 10 and 19.
The Provincial Police Region 9 seized 32 guns including two M16 rifles; the Southern Border Provinces Police Operation Centre nabbed 162 drug suspects along with illicit drugs – 4,305 yaba pills, 20.85 grams of heroin, 47.57 grams of marijuana, 1,020.29 kilograms of krathom leaves, and 2.73 grams of “ice”.
Officers also arrested eight gun-related offenders along with 18 guns, including three M16 rifles and apprehended nine people who were wanted in criminal cases.
Police also reported the extra-judicial killing of four national security suspects during the October 13 search in Songkhla’s Saba Yoy district. They were Abdulwahub Ratuyahae, Yasa Salae, Rusdin Porsu and Fadlan Sohman.
Three of the dead were wanted for various attacks in the deep South.
The slain suspects were armed with two pistols and two M16 rifles that were also seized.