A conserved interdomain microbial network underpins cadaver decomposition despite environmental variables. Researchers tracked 36 human cadavers across three locations, revealing a phylogenetically distinct, interdomain microbial network that assembles during decomposition, regardless of location, climate, or season. By integrating metagenome-assembled genome data with metabolomics, they identified links between taxonomy and function. This universal network of microbial decomposers is characterized by cross-feeding to metabolize labile decomposition products. Key bacterial and fungal decomposers are rare in non-decomposition environments and appear unique to the breakdown of terrestrial decaying flesh, including humans, swine, mice, and cattle, with insects likely playing a role in dispersal. The observed lockstep of microbial interactions supports a robust microbial forensic tool for predicting the time since death. Decomposition is a foundational process on Earth, recycling dead biological material and supporting ecosystem functions. Microbial networks underpin organic matter breakdown, yet their ecology remains poorly understood. While DNA-based assessments of decomposer communities have been made in plant litter and some mammals, little is known about how decomposer communities assemble, interact, or function in ecosystems. Understanding how animal remains decompose is in its infancy due to historical focus on plant litter, which dominates decomposing biomass globally. However, animal biomass contributes significantly to ecosystem productivity, soil fertility, and other functions. The study used three anthropological facilities in the U.S. to investigate microbial decomposer community assembly and function across different climates and seasons. They found that a universal microbial decomposer network assembles despite environmental effects, with increased metabolic efficiencies to process lipid- and protein-rich compounds. Key decomposers are also found in swine, cattle, and mouse carrion, suggesting they are not human-specific but likely general to mammal or animal carrion. The universal microbial network underlies a robust microbial-based model for predicting PMI. The study found that microbial decomposer communities are influenced by stochastic and deterministic processes. Decomposition microbial ecology is influenced by microbial interactions and environmental conditions. A conserved interdomain microbial network underpins cadaver decomposition despite environmental variables. The study also demonstrated the potential of microbiome tools in forensic science for accurately predicting PMI. The predictive models showed generalizability by accurately predicting PMI of independent test samples from various locations and climates. The best-performing model accurately predicted PMI within ±3 calendar days, which is useful for forensic investigations. The study highlights the importance of understanding microbial ecology in decomposing human cadavers and its implications for carbon and nutrient budgets and ecosystem models. The findings suggest that key microbial decomposers are likely inoculated by insects and may contribute to society by providing a new forensic tool and potentially modulating decomposition processes in agricultural and human death industries.A conserved interdomain microbial network underpins cadaver decomposition despite environmental variables. Researchers tracked 36 human cadavers across three locations, revealing a phylogenetically distinct, interdomain microbial network that assembles during decomposition, regardless of location, climate, or season. By integrating metagenome-assembled genome data with metabolomics, they identified links between taxonomy and function. This universal network of microbial decomposers is characterized by cross-feeding to metabolize labile decomposition products. Key bacterial and fungal decomposers are rare in non-decomposition environments and appear unique to the breakdown of terrestrial decaying flesh, including humans, swine, mice, and cattle, with insects likely playing a role in dispersal. The observed lockstep of microbial interactions supports a robust microbial forensic tool for predicting the time since death. Decomposition is a foundational process on Earth, recycling dead biological material and supporting ecosystem functions. Microbial networks underpin organic matter breakdown, yet their ecology remains poorly understood. While DNA-based assessments of decomposer communities have been made in plant litter and some mammals, little is known about how decomposer communities assemble, interact, or function in ecosystems. Understanding how animal remains decompose is in its infancy due to historical focus on plant litter, which dominates decomposing biomass globally. However, animal biomass contributes significantly to ecosystem productivity, soil fertility, and other functions. The study used three anthropological facilities in the U.S. to investigate microbial decomposer community assembly and function across different climates and seasons. They found that a universal microbial decomposer network assembles despite environmental effects, with increased metabolic efficiencies to process lipid- and protein-rich compounds. Key decomposers are also found in swine, cattle, and mouse carrion, suggesting they are not human-specific but likely general to mammal or animal carrion. The universal microbial network underlies a robust microbial-based model for predicting PMI. The study found that microbial decomposer communities are influenced by stochastic and deterministic processes. Decomposition microbial ecology is influenced by microbial interactions and environmental conditions. A conserved interdomain microbial network underpins cadaver decomposition despite environmental variables. The study also demonstrated the potential of microbiome tools in forensic science for accurately predicting PMI. The predictive models showed generalizability by accurately predicting PMI of independent test samples from various locations and climates. The best-performing model accurately predicted PMI within ±3 calendar days, which is useful for forensic investigations. The study highlights the importance of understanding microbial ecology in decomposing human cadavers and its implications for carbon and nutrient budgets and ecosystem models. The findings suggest that key microbial decomposers are likely inoculated by insects and may contribute to society by providing a new forensic tool and potentially modulating decomposition processes in agricultural and human death industries.